Method and apparatus for aligning an illumination unit to a slider for a magnetic recording device

ABSTRACT

An alignment method for bonding a first component to a second component is described. A plurality of sliders having alignment markers are substantially aligned to the alignment markers of a plurality of illumination units and then positioned into alignment by moving the slider with respect to the illumination unit by an offset. The offset is calculated by scanning a light source around the waveguide to determine the distance that the alignment markers of the slider are separated from the alignment markers on the illumination unit.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/969,782, filed on Aug. 19, 2013, which claims priority to U.S.Provisional Patent Application No. 61/846,868 entitled “METHOD ANDAPPARATUS FOR ALIGNING AN ILLUMINATION UNIT TO A SLIDER FOR A MAGNETICRECORDING DEVICE, filed on Jul. 16, 2013 for Chee Kheng Lim, both ofwhich are incorporated herein by reference.

BACKGROUND

Heat assisted magnetic recording (HAMR) typically uses a laser source toprovide additional energy to magnetic media during the data writingprocess. The laser source may include a submount assembly, whichtogether is referred to as a Chip-On-Submount-Assembly (COSA). The COSAis attached to the back of a conventional magnetic head slider and lightenergy from a laser diode chip is guided to the air bearing surfacethrough a waveguide to heat the magnetic media.

To ensure that the laser diode output is efficiently coupled to thewaveguide on a slider it is desirable to accurately bond the slider tothe laser source. Aligning the laser source and the slider to thedesired position is time consuming and prone to error. The manufacturingyield for fabricating magnetic devices may be adversely affected due tomisalignment of the laser with respect to the slider. Therefore, a needexists for a simplified alignment method that accurately aligns a sliderto an illumination unit and that improves manufacturing yield.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram that illustrates an alignment method accordingto one embodiment.

FIG. 2 is a perspective view of a slider with alignment marks and awaveguide.

FIG. 2A is an enlarged view of section W of FIG. 2.

FIG. 3 illustrates an alignment apparatus that includes an activealignment station and a passive alignment station according to oneembodiment.

FIG. 4 illustrates a laser irradiating the area of a waveguide in across-track direction.

FIG. 5 illustrates a COSA chip irradiating the area of a waveguide in adown-track direction.

FIG. 6 is a perspective view of a slider being bonded to a chip.

FIG. 7 illustrates a system according to one embodiment.

DETAILED DESCRIPTION

A hybrid active and passive alignment method is provided for bonding afirst and second component together for use in a magnetic recordingdevice. In certain embodiments, the method achieves high throughputwithout compromising the alignment accuracy and alignment yield of thecomponents. In one embodiment, the first component comprises a sliderand the second component comprises an illumination unit.

FIG. 1 is a flow diagram illustrating a method for aligning a firstcomponent to a second component according to one embodiment. The processstarts by establishing an initial alignment position of a slider viablock 110. This involves identifying the location of the alignmentmarkers on a reference slider, and then substantially aligning theslider's alignment markers to alignment markers on an illumination unit.The initial alignment position will later be used to calculate an offsetfor passive alignment.

The process proceeds by irradiating a waveguide on a reference sliderwith a laser or an illumination unit according to block 120. Either acollimated or uncollimated illumination unit may be used. A detectormonitors the light intensity output by the laser via block 130 to locatean optical alignment position. Upon establishing optical alignment, anoffset may be calculated via block 140. Each slider is subsequentlymoved from its initial alignment position by the offset prior to bondingto the illumination unit in accordance with block 150. Then the slidersare separately bonded to a corresponding illumination unit via block160.

The method of FIG. 1 will be discussed in further detail in associationwith FIGS. 2-7. FIG. 2 is a simplified drawing of a slider 200 having awaveguide 250 on top surface 210. The waveguide 250 is located betweenalignment markers 220 on the slider 200, and extends from top surface210 to bottom surface 215. Although in other embodiments, the waveguide250 is not necessarily located between the alignment markers 220.

FIG. 2A is an enlarged view of section W of FIG. 2. Distance drepresents an offset, which corresponds to the manufacturing toleranceor variance of slider 200, and may include other manufacturingtolerances. Thus, offset d reflects the misalignment of waveguide 250from alignment markers 220 on slider 200. Offset d is used to preciselyalign other sliders 200 to illumination units 285 (discussed inreference to FIG. 5) based on the distance separating the initialalignment position and the optical alignment position of a referenceslider. The reference slider resembles slider 200 and is selected fromsliders manufactured from the same wafer or wafer section. The manner bywhich various elements on slider 200 are located is described below inreference to FIG. 3.

The alignment apparatus 300 of FIG. 3 includes two stations: ameasurement station 305 and a bonding station 310. Measurement station305 may utilize a high resolution vision recognition camera to locatealignment markers 220 on a reference slider. The alignment markers 220are then used to approximately determine the waveguide position, sincewaveguide 250 is not generally visible even with a high resolutionoptical system. The corrected alignment position is later determined bythe active alignment portion of alignment apparatus 300.

The waveguide position coordinate data determined at measurement station305 may be dynamically transmitted to the bonding station 310 to ensurethat slider 200 is adjusted by the offset d prior to bonding. In certainembodiments, this adjustment substantially increases the likelihood thatthe output of a laser is correctly aligned to waveguide 250. Slider 200may then be eutectic bonded to illumination unit 285 using aconventional soldering process or other adhesion method.

FIGS. 4 and 5 illustrate two different alternative illumination units(245 and 285) that are suitable for implementing one embodiment of thepresent alignment method. FIG. 4 illustrates a laser 245 that irradiatesthe slider 200 while scanning top surface 210 in a down-track direction.In some embodiments, the beam may be scanned in both a cross-track and adown-track direction. During irradiation, the slider may beincrementally moved with respect to the illumination unit from theinitial alignment position. In addition, while slider 200 is beingirradiated around waveguide 250, a detector 212 measures the lightintensity exiting surface 215, which is the bottom surface of slider 200(opposite top surface 210) in accordance with one embodiment of block130. In some embodiments, lasers suitable for scanning via block 120operate at a wavelength of approximately 830 nm. Although the laser 245is illustrated as emitting a collimated beam, it will be appreciatedthat an uncollimated source may be used as well. If a collimated sourceis used to scan the light beam, then the distance from the source to thewaveguide 250 may not be critical. However, when an uncollimated sourceis used, in certain embodiments, the uncollimated source may be operatedat a power level between 1-10 milliwatts.

In alternative embodiments, illumination unit can be a COSA chip 285 asshown in FIG. 5. When a COSA chip 285 is used as the illumination unit,the distance between alignment markers 240 and the waveguide 250 can beless than 100 micrometers, due to the divergence of the beam from thelaser diode chip. In one embodiment, COSA chip 285 is scanned in adown-track direction relative to slider 200. In other embodiments, COSAchip 285 is scanned in both cross-track and down-track directionsrelative to slider 200. In several embodiments, the waveguide positionis identified when detector 212, such as a photodiode, detects themaximum light output from the slider 200.

Once the waveguide 250 is precisely located, the offset d of waveguide250 from alignment markers 220 is calculated. It is desirable to computeoffset d because of process variations during manufacturing that tend toaffect alignment accuracy. Since the waveguide 250 and alignment markers220 are fabricated separately, and a number of layers separate waveguide250 from alignment markers 220, component variations are ofteninevitable. Although the exact position of waveguide 250 varies, thelocation of the waveguide 250 is not measured on every slider 200. Withthe offset d calculated, slider 200 is ready for bonding.

Bonding station 310 resembles a passive alignment system due to theabsence of an illumination source. In block 150, a pick and place robotmoves the alignment markers 240 of illumination unit 285 intosubstantial alignment to alignment markers 250 as shown in FIG. 6. Nextthe position of slider 200 is adjusted by the previously calculatedoffset via block 150. Then the slider and illumination unit 285 arebonded together via block 160.

The measurements performed at measurement station 305 can be used tocompensate for any offset d needed to accommodate component variation.For example, some sliders may vary in the thickness of layers separatingwaveguide 250 and markers 220, or have waveguides that are at a distanceof ≧0.02 microns from alignment markers 220. Such variations can bedetected before or after bonding at bonding station 310. For example, todetect a component variation prior to bonding, an alignment marker onslider 200 is used as a reference point (reference marker). Then theintensity of the light beam exiting the waveguide 250 is evaluated by adetector 212. When the maximum light intensity is located, opticalalignment is established. Upon determining the optical alignmentposition, the distance from the alignment marker 220 is measured toascertain if any large component variations are present. If variationsexceeding 0.1 microns from one slider to another slider, then thesampling frequency of the waveguide 250 is increased. Alternatively, apost-bond optical test system can be used to determine the amount oflight that is coupled into the waveguide. Variations among differentparts can lead to significant reduction in the light intensity outputfrom the waveguide, to thereby indicate that such variations areaffecting the alignment accuracy. At which point, the next slider wouldbe evaluated in measurement station 305 prior to bonding any furtherparts in bonding station 310.

In certain embodiments, it is not essential to pre-measure the waveguideprior to passive alignment at bonding station 310 if the waveguide isknown to be within +/−0.1 microns of alignment markers 220. Thus, insuch embodiments, a throughput of up to 100 sliders is possible beforethe waveguide is measured again. In this manner, the waveguide positiondata from the reference slider can substantially minimize misalignmentdue to part-to-part variation.

Accordingly, in certain embodiments, high throughput may be achieved bymeasuring the waveguide position in a sampling manner. For example, thewaveguide position can be measured in one of every ten sliders. In otherembodiments, the waveguide position can be measured in one of every 100sliders. The frequency of the waveguide measurement will depend on theoffset variation from the waveguide 250 to the alignment markers 220.The waveguide coordinates pursuant to block 140 are then dynamicallytransmitted to the bonding station to perform the passive alignmentprocess. In some embodiments, block 140 contributes to high throughputyield by periodically sampling sliders to compute an offset, rather thanmeasuring optical alignment positions on every single slider beforebonding each slider 200 to an illumination unit 285.

FIG. 7 summarizes yet another embodiment of the present disclosure. Atthe start of the system 700, a vision camera 710 can be used to identifythe location of alignment markers 220 on slider 200. Once alignmentmarkers 220 are identified, the slider 200 is transferred to measurementstation 715 to measure the waveguide position. Measurement station 715is analogous to station 305, discussed in reference to FIG. 3; howeverthe two measurement stations are not the same. At measurement station715, the degree of variation from part to part can be assessed. Incertain embodiments, the offset d will be known after the waveguideposition is measured at measurement station 715. Then a processor, orother calculating apparatus (not shown), can be used to calculatewhether offset d exceeds an acceptable threshold (offset threshold), orotherwise determine if the sampling frequency should be increased. Thewaveguide sampling frequency can be adjusted depending on the level ofcomponent variation detected. For example, if large part-to-partvariation is detected, more frequent measurement will be activated toaccount for the passive alignment offset. On the other hand, if atrivial variation in waveguide position is determined by the processor,then a less frequent measurement may be needed. In one embodiment,intelligence software can be used to automatically adjust the samplingfrequency.

Once the processor determines whether a variation is acceptable or not,then the alignment process can proceed in either of two ways asindicated at decision block 725. If no variation or a trivial variationis detected, then the system will bond the slider to the illuminationunit at bonding station 730. Subsequently, the bonded slider andillumination unit can then be integrated into a magnetic device viablock 750. After product integration, bonding of additional sliders maycontinue based on the originally calculated offset d. On the other hand,a significant variation may be detected after bonding at testing station740. If testing determines that the bonded slider varies substantiallyfrom the reference slider, then system 700 will proceed to beginmeasuring the alignment markers and waveguide position on a referenceslider via block 735. In other words, if block 725 identifies acomponent variation that exceeds the offset threshold, then a new offsetd is determined using a reference slider via block 735.

By performing several embodiments described above, alignment ofcomponents can be achieved with accuracy and high throughput. The methodand system of the disclosure are primarily designed for submicronbonding accuracy. It is estimated that by adopting the aforementionedhybrid alignment system that the bonding cycle for aligning multiplecomponents may be reduced by about 3-5 seconds. As a result, the diskdrives and other devices fabricated with components aligned by themethods described herein may have improved performance.

What is claimed is:
 1. A system for aligning a slider to an illuminationunit comprising: an active alignment apparatus for substantiallyaligning a slider to an initial alignment position relative to theillumination unit, wherein the active alignment apparatus includes alight source, a detector, and a measurement station, and wherein thelight source irradiates a reference slider while the detector evaluateslight emitted from a bottom surface of the reference slider to determinea position of optical alignment; a measurement station that periodicallymeasures an offset corresponding to the distance from the initialalignment position to the optical alignment position of a referenceslider; a passive alignment apparatus that includes a bonding stationfor attaching a plurality of sliders to a plurality of illuminationunits, and a testing station that periodically checks for misalignmentof sliders and illumination units by measuring the amount of lightcoupled into the waveguide of the slider after being bonded to theillumination unit.
 2. The system of claim 1, wherein the light source ispart of the illumination unit.
 3. The system of claim 1, wherein theillumination unit is not part of the light source.